Life depends on water. Our entire living world—plants, animals, and humans—is unthinkable without abundant water. Human cultures and societies have rallied around water resources for tens of thousands of years—for drinking, for food production, for transportation, and for recreation as well as inspiration.
Large portions of Earth's dry land are arid and experience shortages of water. Such shortages become more acute each year in many regions as a result of population growth, climate changes and environmental pollution. The aquifers of the world on which agriculture depends in drier regions are being drained of their ground water faster than the reserves can be replaced by natural percolation of rainfall and runoff. Water shortage results in increased competition for water sources to satisfy the needs of agriculture, industry, and community, which places a great stress on existing water supplies. These conditions create an enduring need for a new water source for use in agriculture and forestry that would reduce pressure on existing supplies, potentially reversing the depletion of reservoirs and ground water, decrease the likelihood of forest fires and resulting soil erosion, and potentially open new lands for cultivation and human habitation.
Water shortage in arid areas can be addressed in two ways: 1) improved management of existing water resources and 2) development of new resources. Resource management techniques such as conservation and irrigation have been already put into common practice in many arid and drought affected areas. However, the development of new water resources has been rather slow. Possible new resources include sea water desalination and extraction of water from atmospheric air. Desalination is not generally suitable for many inland areas as it requires easy access to sea water. In addition, desalination is very capital and energy intensive, requires an acceptable method for disposal of brine, and construction of new plants is subject to many environmental regulations.
One frequently overlooked approach is direct extraction of water from atmospheric air. Each year some 5.8.times.10.sup.14 m.sup.3 (4.7.times.10.sup.11 acre-feet) of water evaporate from the land and ocean surfaces. The resulting moisture in the air acting through natural rainfall replenishes water in the rivers, lakes and aquifers. In particular, part of the huge amount of water evaporated in the oceans is carried by wind to arid regions of the world. Half the total atmospheric water is contained in the lower 6,000 ft of the atmosphere. For example, 1 m.sup.3 of air at ambient temperature and 40% humidity contains about 11 grams of water. And yet atmospheric air, a major renewable source of fresh water, is under-exploited by man.
One method for direct extraction of water from atmosphere that has been practiced since the 1940's is cloud seeding which can significantly improve rain yield. However, this method requires availability of dense low clouds and thus it is limited to certain coastal areas and the wet season of the year.
A more direct method would target the omnipresent moisture in atmospheric air and would be available during the hot and dry summer months. It is well known that air in many arid coastal areas is very humid. However, measurements show that even the dry air in the desert contains enough moisture that could be extracted and used as a water source of agriculture and forestry.
The idea of reducing atmospheric moisture into liquid water is not new. Patent literature worldwide contains some 30 patents for methods and devices in this area. However, vast majority of these concepts is characterized by complexity (including the need for refrigeration, blowers, high-pressure chambers, and/or large tracts of real estate) and motive power. As a result, most of these concepts remained only on paper and none has been practical enough to win commercial acceptance.
There are several approaches for direct extraction and liquefication water from atmospheric air namely 1) direct condensation at ambient pressure, 2) direct condensation at elevated pressure, and 3) adsorption onto sorption medium followed by secondary extraction (usually by heating) followed by condensation.
Direct condensation at ambient pressure is an approach in which atmospheric air is presented with a condensing surface cooled to below a dew point. Contact with the surface cools the air and part of its water vapor content is reduced to liquid appearing on the surface as a condensate. Heat released in condensation must be continuously removed from the condensing surface otherwise the surface will warm up to above the dew point thereby inhibiting further condensation. In nature, dew commonly appears on objects that cool below the dew point by radiating some of their thermal energy into space and thus cooling below temperature of ambient air and the dew point. For this phenomenon to occur, the separation of air temperature and the dew point must be rather small (typically a few degrees Centigrade). Thermal radiation processes can be enhanced by man-made means as disclosed by Riley et al in U.S. Pat. No. 3,318,107. However, this apparatus too requires the separation of air and dew point temperatures to be rather small, making it unusable in most atmospheric conditions, especially in dry regions.
To condense water from air having significant temperature and dew point separation requires a more efficient heat removal than rendered by thermal radiation. Courneya in U.S. Pat. No. 4,351,651 discloses an apparatus which draws ambient humid air into an underground heat exchanger rejecting heat into soil. This invention assumes that the temperature of soil is significantly lower than the temperature of ambient air. While this is generally true in the daytime, the air temperature-dew point separation at this time is also quite significant except in cases of extremely high humidity. Such conditions of very high humidity are rather rare in dry climates. At nighttime, the ambient air is usually cooler than the temperature of the soil and the apparatus would have little chance of working. Other approaches involving passive cooling by high-altitude air or sea water have been disclosed by Phela, Jr. et al in U.S. Pat. No. 3,746,867 and by Gerard et al in U.S. Pat. No. 3,498,077 respectively have similar limitations.
To overcome the limitations of passive cooling, a variety of condensing devices employing refrigeration have been proposed. For example, Rosenthal in U.S. Pat. No. 5,857,344 discloses an apparatus for condensing atmospheric moisture using a vapor compression type refrigeration. Similar approach is also disclosed by Littrell in U.S. Pat. No. 4,892,570. To overcome the limitations of expensive and noisy machinery associated with this type of refrigeration, several condensing devices have been proposed using solid-state refrigerators based on the Peltier effect. Peltier coolers are compact, quiet, have no moving components, but are somewhat more expensive and less thermodynamically efficient than vapor compression units. Devices and methods disclosed by Biancardin in U.S. Pat. No. 4,315,599, Wold in U.S. Pat. No. 5,601,236, and Peeters et al. in U.S. Pat. No. 5,634,342 all use Peltier effect condensing units and are intended for providing water to plants.
While refrigeration type condensing units are very capable in reducing atmospheric moisture to liquid water (as exemplified by ordinary household air condition unit on a humid day), their water output is not commensurate with their initial and operating costs. The key reason for the latter is that removal of moisture by condensation from air with significant temperature-dew point separation requires cooling large quantities of air to extract rather small amount of water. In arid regions where the need for new water sources is the greatest; the air temperature-dew point separation is quite significant (20-40 degrees Centigrade in the daytime), which would make the operation of condensing devices prohibitively expensive. Using solar cells to generate power required for the refrigerator (as disclosed, for example, by above-mentioned Wold) is hardly satisfactory since electric power from solar cells is rather expensive.
Another approach to direct extraction of water from atmospheric air is condensation at elevated pressure. It is well known that when atmospheric air is compressed above ambient pressure, its dew point increases and condensation can occur at ambient temperature. This phenomenon is actually a hindrance in many compressed air installations and various means have been devised to dehumidify compressed air in industrial application. See for example Ewing et al. in U.S. Pat. No. 2,077,315 or Alderson et al. in U.S. Pat. No. 3,226,948. Devices and methods for direct extraction of water from air using condensation at elevated pressure have been disclosed by Spletzer et al. in U.S. Pat. Nos. 6,230,503, 6,360,549, and 6,511,525.
One common challenge all water devices using condensation at elevated pressure must overcome is adiabatic heating of air during compression. This heat must be removed from compressed air lest the desired reduction in air temperature-dew point separation would require even higher pressures to attain. This heat, unless recovered through a heat exchanger, is lost and must be made up by some of the mechanical work required for compression. Regardless of the approach taken, all of the inventions based on this approach require a compressor and significant motive power. This makes it very challenging to realize these inventions in compact, lightweight, inexpensive devices operating mostly on renewable sources of energy.
Yet another approach for extraction of water from atmospheric air uses sorption materials suitable for preferential trapping of water molecules by either physical adsorption such as for example exhibited by molecular sieves, or chemical adsorption such as for example exhibited by lithium chloride. There is a long list of such suitable materials, see for example, D. K. Veirs et al, “Technical Basis for Packaging Glovebox Moisture Content,” LA-UR-02-560, Los Alamos National Laboratory (undated). Once the sorption material is saturated with water to desirable level, application of heat drives the adsorbed water vapor out and liquid water can be obtained by condensation. There is a significant number of inventions based on this technique. For example, Groth et al. in U.S. Pat. No. 4,146,372 discloses an apparatus that receives humid air at night and uses suitable sorption medium to extract moisture from it. Night air is also used to cool down a condenser with a large thermal mass. In the daytime, solar heating is used to drive the water vapor out of the sorption medium. Blowers are used to direct desorbed water vapor into the condenser where some of the water is condensed. Note that desorbed water vapor is diluted with fresh air which makes desired condensation more difficult. This apparatus is envisioned on a very massive scale with vertical separation as much as 200 meters between various components. It requires motive power to drive blowers for inducing night air into the device and to move moist air with desorbed water vapor to the condenser. Hussmann in U.S. Pat. Nos. 4,342,569 and 4,345,917 disclosed various improvements to Groth and including a recirculation of air transporting desorbed water vapor to the condenser.
Michel et al. in U.S. Pat. No. 4,285,702 discloses an apparatus and method similar to that of Groth and Hussmann except that it can be realized in a much smaller apparatus. Air transporting desorbed water vapor from the sorption medium to the condenser is recycled within the device using a blower. Other similar devices of this type are disclosed in U.S. Pat. No. 4,299,599 and U.S. Pat. No. 4,365,979 of Tokeyama et al. Clarke in U.S. Pat. No. 5,233,843 and Conrad in U.S. Pat. No. 6,156,102 disclose adsorption type devices using liquid sorption media.
Krumsvik in U.S. Pat. No. 5,846,296 discloses a pyramid-shaped apparatus with transparent walls containing sorption medium in its lower portion and a condenser in its upper portion. At night, the unit admits humid air which deposits moisture in the sorption medium. In the daytime, solar heating is used to drive the moisture from the sorbant and the vapor is allowed to rise up to the condenser where it is turned into liquid. The arrangement of sorption medium in the pyramid is not conducive to obtaining desorption temperatures much beyond outside air temperatures since much of medium is not directly irradiated by the sun and a lot of the heat is lost through the pyramid walls. Hence only a small portion of adsorbed water can be actually desorbed. Furthermore, this device has large empty volume filled by air. This means that a large portion of desorbed water will be expended in merely used to increase humidity of air inside the pyramid. Since this air is also heated, its dew point will correspondingly increase. Thus the air can accommodate more moisture without condensation. Because in a steady state, desorption cannot proceed faster than condensation, it is difficult to see how this device, despite its large size, could be conducive to water production at high rates. Similar apparatus is also disclosed by Alexeev et al. in U.S. Pat. No. 6,116,034.
Tsymerman in U.S. Pat. No. 6,336,957 discloses an adsorption type apparatus and method for recovery of water from atmospheric air having a chamber with two parts; one housing the sorption medium and the other housing a condenser. The two parts of the chamber are connected by plumbing. A fan blows outside air through the sorption medium while the medium is cooled by imbedded heat exchanger. The chamber is then isolated from outside air and the sorption medium is heated using the imbedded heat exchanger to the point where the internal pressure rises significantly above ambient pressure. When a pressure relief valve is blown, partial vacuum is suddenly created in proximity of the condenser, thereby creating a pressure gradient that starts delivering desorbed moisture to the condenser. Because the pressure relief valve exhaust residual air from the chamber, subsequent condensation takes place at partial vacuum. The condenser is cooled by unspecified external means. The chamber must be constructed so that it can withstand elevated pressure as well as vacuum.
Methods and devices disclosed in all of the above prior art are either not conducive to operation in dry regions, and/or not suitable for production of water at significant rates, and/or require costly mechanical compressors or complex and expensive refrigeration, and/or cannot be implemented in compact portable units, and/or require large amounts of motive power.
Hence, there is need for new devices and methods that could lead to compact, lightweight, robust, inexpensive, transportable units with few moving parts and operating mostly on renewable sources of energy.
It is therefore one object of the present invention to provide a sustainable source of irrigation water for agriculture, including areas where no water resources exist or are not economically viable. As an alternative to other forms of irrigation, the invention provides salt-free water, thereby decreasing the salt-content in the soil, reducing injury to crops plants, and improving quality of certain crops (especially wine grapes). Another potentially important benefit to agriculture will be livestock watering stations for remote areas where local water supplies are non-existent or unreliable.
Another object of the present invention is to provide an alternate source of water thereby reducing the competition for existing water resources used by current irrigation techniques. Besides providing immediate relief, this would also allow returning reservoirs and aquifers to their normal level, making them available for combating future droughts while increasing recreation and tourism. In addition, increased ground water levels will also improve the health of forests, enabling them to endure droughts, and be less susceptible to wildfires and soil erosions. Furthermore, when deployed in forestry settings, the invention can increase the survival of newly planted trees and help in natural revival of the forest.
Shortage of water impedes the development of the vast areas of arid land. It is yet another object of the present invention to provide a suitable water supply in these areas and open them to agriculture and human habitation.
It is yet another object of the present invention to provide a self-contained, autonomous, transportable, inexpensive, environmentally friendly device for the autonomous long-term irrigation of plants and trees in agricultural, forestry, and household settings.
Still another object of the invention to provide a method and apparatus for producing liquid water from ambient air using low energy input.
Yet another object of the invention to provide a method and apparatus for producing liquid water from ambient air using solar power.
Yet another object of the invention to automatically water plants to support plant growth.
Yet another object of the invention to provide a source of water in arid regions.
Yet another object of the invention to provide livestock watering stations for remote areas where local water supplies are non-existent or unreliable.
Yet another object of the invention to provide a source of water for household use in arid areas.
Yet another object of the invention to provide a source of water for watering of indoor plants.
It is yet another object of the invention to provide method for reducing susceptibility of growing microorganisms inside an apparatus for producing liquid water from ambient air.